This invention relates to a system for treating flowable food products in the course of drying, heating, reacting and cooking. More specifically, the present invention relates to a method and thermal processor which is well suited for thermal processing of starch and starch-bearing products whereby the material can be treated in some fashion in the course of its progression through an apparatus to achieve the desired reaction, for example, gelatinization, preconditioning, and other modifications before extrusion, final drying or further processing.
Starch and starch-bearing products are a staple of commerce and represent one of the main ingredients in a wide variety of food products. In commercial practice, the common technique for thermoprocessing of starch and starch-bearing products before extrusion, final drying, or further processing, is based on utilization of steam pressure cookers of the type generally described, for example, in the brochure 5430 of Andritz Sprout-Bauer Co. This process suffers from a number of disadvantages. Firstly, the step of preconditioning/thermal treatment of the product with the purpose of partial gelatinization and/or cooking of the starch is conducted in the pressurized vessel with live steam injection as the only source of heat supply to the product. Since the gelatinization reaction rate (or degree/percentage of gelatinization in the given thermal processing time) depends on the processing factors, such as temperature and product moisture content, the prior art methods based on the live steam injection in the cooker are incapable of precisely controlling the optimum correlation between the critical process parameters. This method will, therefore, not provide a required amount of gelatinized starch in different products to meet specific needs.
Another problem associated with the known process is a relatively long residence time due to inefficient heat and mass transfer in an insufficiently agitated paddle-type or screw processor that operates with a bed of material. As a result, the treated product is heterogeneous in terms of degree/percentage of gelatinization.